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Original question:

TPS27S100: I out explanation in external current limit calculation

TPS27S100: FLT pin latching even after short circuit removed.

Sooraj P
Prodigy 90 points
Part Number: TPS27S100

Tool/software:

Hi

The datasheet says below paragraph.

7.3.4.1 Short-to-GND and Overload Detection

When the switch is on, a short to GND or overload condition causes overcurrent. If the overcurrent triggers either
the internal or external current-limit threshold, the fault condition is reported out. The microcontroller can handle
the overcurrent by turning off the switch. The device heats up if no actions are taken. If a thermal shutdown
occurs, the current limit is IILIM(TSD)to keep the power stressing on the power FET to a minimum. The device
automatically recovers when the fault condition is removed.

what is the fault recovery time here?

when I short circuited Vout and ground, FLT pin is going low as expected, but it not recovering even though the short circuit is removed. 

why is it like this?

Regards 

Sooraj P

  • 0
    TI__Expert 7921 points

    Hi Sooraj,

    We cannot guarantee a fault recovery time. Auto-recovery depends on the temperature of the device and if the fault is removed. It is possible that the temperature of the device is not low enough for auto-recovery. You can also try toggling the EN pin to see if the output comes back on without a fault condition. Please see below.

    Thanks,

    Rishika Patel 

  • 0
    Prodigy 90 points

    Hi

    Thank you for the reply. 

    What is the voltage, FLT pin will give during normal condition (without any fault) I am getting 4.5 volts.

    and is there any way I can tweak the circuit such a way that open load protection is disabled?

    Regards

    Sooraj P

  • 0 in reply to Sooraj P
    TI__Expert 7921 points

    Hi Sooraj,

    The maximum recommended voltage that should be on the FLT pin is 5V as it is pulled high during normal condition and low when a fault occurs. The fault pin can be pulled up to 5V by the LDO If you are using the EVM or an external power supply. 

    Since the open load protection is part of diagnostics, the only way to disable it would be to turn off the DIAG_EN pin which would remove all of the protections (please see the fault table and below for all of these features). 

    Thanks,

    Rishika Patel 

  • 0 in reply to Rishika Patel
    Prodigy 90 points

    Thank you, Rishika, for the reply 

    can you suggest me a part with same electrical specs as tps27s100, with adjustable external current limit via resistor and with (power good indication)

    which give a logic low signal only during overload/short circuit event.

    Regards

    Sooraj P

  • 0 in reply to Sooraj P
    TI__Expert 7921 points

    Hi Sooraj,

    The TPS27S100 does have the current limit feature via external resistor. Do you mean that you do not want open load detection at all or any other protection besides overload/short circuit?

    Thanks,

    Rishika Patel 

  • 0 in reply to Rishika Patel
    Prodigy 90 points

    Hi Rishika

    Yes , I am looking for a part which give a logic low signal when short circuit happens. And current limit feature via external resistor.  we don't require open load protection, since our customers may leave the channel open. 

    My existing IC has power good feature where when short circuit happen i will get a low signal through power good pin. I am looking for something like this

    Regards

    Sooraj P

  • 0 in reply to Sooraj P
    TI__Expert 7921 points

    Hi Sooraj,

    I apologize for the confusion, so disabling diagnostics would make it so faults are not being reported. The current limit and thermal shutdown/swing would still be active. You can use the B version of the TPS27S100 device and make sure to NOT connect an external pull-up resistor from the output to the power supply, so that off-state open-load detection is not available. During the on-state, the user judges if there is an open-load condition. Let me know if you have any more questions.

    Thanks,

    Rishika Patel